An overhead crane for hoisting and moving containers can be used in both sea port container terminals and inland port terminals. A sea port container terminal usually comprises three areas. A strip, which is situated directly on the water and has a width of approximately 50 meters, is also referred to as the ship to shore (STS) area. This is the area in which the containers are transferred from the ocean-going vessels which have entered the harbour onto land using the large cranes on board, also referred to as STS cranes.
Directly behind the STS area, on the landward side of the STS area, there is a transfer zone where the containers are taken to a storage yard by means of so-called straddle carriers or automated guided vehicles (AGV's). This area is approximately 100 to 120 meters wide. The storage yard is also referred to as the stack area.
Depending on the size of the terminal and the transportation means, the width of the stack area varies between 300 and 700 meters. The length of the stack area is usually equal to the length of the quayside.
Over the course of the last 20 years, the loading and unloading speed of the STS cranes has steadily increased in order to ensure that the vessels are moored on the quayside for as short a time as possible. This has resulted in congestion in or just in front of the stack area, requiring the creation of intermediate buffers.
It is an object of the invention to increase the processing speed in the stack area compared to the current situation. It is another object of the invention to increase the stacking capacity while not increasing the surface area. A greater stack density saves valuable space. Stacking the containers higher does increase the stack density, but, with the crane systems which are currently being used in the stack area, the so-called stack crane systems, it is disadvantageous in terms of the time (“digging time”) which is spent when containers from the bottom layers have to be transported first.
The stacking height of stacks of containers which are transported across the terminal using straddle carriers is usually 1 over 3. This means that the stack comprises three layers and that there is one layer which is reserved for transport movements above these.
With cranes which are known as rail-mounted gantry cranes (RMGs), i.e. cranes which may be defined as gantry cranes travelling on rails which have been laid at ground level, the stacking height is already 1 over 4 or even 1 over 6, despite the abovementioned drawback of the increasing “digging time”.
For the sake of completeness, it should be noted that the effective processing speed in a stack is determined to a significant degree by the number of cranes, the speed of the cranes, both when travelling and when hoisting, the stack density, the degree of automation, the susceptibility to failure, the redundancy and the length-to-width-ratio of the stack lanes.
As has been indicated above, the cranes in the stack areas of container terminals are often configured as RMGs which travel on rail systems which have been installed at ground level. These RMGs have the drawback that they cannot pass each other, so that the working area of an RMG is linked to the seaward side or the landward side of a terminal. Another drawback is the fact that the gantry structure has a considerable dead load and therefore it requires a large amount of power to drive the crane. It is quite common to use a dead weight of 150 tonnes to transport a container weighing 30 tonnes. Furthermore, the travelling speed is limited, as the centre of gravity is situated high above the wheels, which is disadvantageous for both the longitudinal stability and the transverse stability and the swinging of the load during transportation.
In order to enable RMGs to pass each other in one lane (also referred to as a track) of the stack area, according to the prior art, an oversized RMG is added which also serves as a replacement in case one of the other RMGs fails. The drawback of this solution is that the additional rail system to accommodate the oversized RMG takes up a great deal of space along the entire length of the lane. Another drawback is the fact that the workload during normal operation is lower for each RMG than is the case with two RMGs in one lane. In lanes with two RMGs, a problem again arises when one of the two RMGs fails, since the RMGs cannot pass each other. In order to solve this problem, a so-called rescue crane has been developed for the current situation, which can be used to pick up a broken-down RMG and move it.
JP 2008/174 374 A discloses a multistory warehouse comprising a container housing zone in each floor, an overhead crane in each floor moving along the container line of the container housing zone, a container delivering zone provided in an end of the container housing zone of the first floor wherein container carry-in/out trucks move, and a spreader elevating zone formed over the container carry-in/out zone so as to vertically move a spreader of the overhead crane of each floor to the container carry-in/out zone.
WO 01/62 656 A2 discloses an empty container storage for the intermediate storage of empty containers, especially in fully automatic container terminals of seaports or river ports, characterised by a full gantry bridge crane that can be automated, traverses the empty container storage, can be moved on an elevated craneway and has a travelling crab that can be moved thereon in the longitudinal direction thereof.